I am assuming that the surface is concrete that you wish to remove the Tar off.
Add kerosene to a strong caustic degreaser, apply with broom and then hit with high temp. The kerosene will not mix with the degreaser, that is why it needs to be applied with a broom but what it will do is cause the tar to flow. The degreaser will help this but also help in stopping the Tar /kerosene mix from staining the concrete elsewhere once it is removed. Do a small section at at time and you will get it sorted.
We clean a premises that runs Tar trucks and the above is the best we have come up with so far but if you have got something better, then I am all ears.